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Bonnie J. Leadbeater, Megan E. Ames, Paweena Sukhawathanakul, Murray Fyfe, Richard Stanwick, Jeffrey R. Brubacher, Frequent marijuana use and driving risk behaviours in Canadian youth, Paediatrics & Child Health, Volume 22, Issue 1, 1 March 2017, Pages 7–12, https://doi.org/10.1093/pch/pxw002
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Abstract
A better understanding of the relations between patterns of marijuana use and driving risks in young adulthood is needed.
Secondary analyses of self-report data from the Victoria Healthy Youth Survey. Youth (baseline ages 12 to 18; N=662; 52% females) were interviewed biannually (on six occasions) from 2003 to 2013 and classified as abstainers (i.e., used no marijuana in past 12 months), occasional users (i.e., used at most once per week), and frequent users (i.e., used more than once a week).
In the frequent user group, 80% of males and 75% of females reported ‘being in a car driven by driver (including themselves) using marijuana or other drugs in the last 30 days’, 64% of males and 33% of females reported that they were ‘intoxicated’ with marijuana while operating a vehicle and 50% of males and 42% of females reported being in a car driven by a driver using alcohol. In addition, 28% of occasional users and also a small proportion of abstainers reported ‘being in a car driven by a driver using marijuana or other drugs in the last 30 days’.
The high frequency of driving risk behaviours, particularly for frequent users, suggest that plans for legalization of recreational use should anticipate the costs of preventive education efforts that present an accurate picture of potential risks for driving. Youth also need to understand risks for dependence, and screening for and treatment of marijuana use disorders is needed.
La consommation fréquente de marijuana et la conduite à risque chez les jeunes Canadiens
Il est nécessaire de mieux comprendre les liens entre les habitudes de consommation de marijuana et la conduite à risque chez les jeunes adultes.
Les auteurs ont procédé à des analyses secondaires de données autodéclarées tirées du sondage sur la santé des jeunes de Victoria. Dans ce sondage, les jeunes (de 12 à 18 ans en début d’étude, n=662; 52 % de filles) ont participé à une entrevue tous les deux ans (à six reprises) entre 2003 et 2013. Ils ont été classés comme abstinents (aucune consommation de marijuana dans les 12 mois précédents), consommateurs occasionnels (consommation maximale d’une fois par semaine) et consommateurs fréquents (consommation plus d’une fois par semaine).
Dans le groupe des consommateurs fréquents, 80 % des garçons et 75 % des filles ont déclaré « avoir été dans une voiture conduite par une personne (y compris eux-mêmes) qui avait consommé de la marijuana ou d’autres drogues dans les 30 jours précédents », 64 % des garçons et 33 % des filles ont affirmé avoir déjà été « intoxiqués » par la marijuana lorsqu’ils conduisaient une voiture et 50 % des garçons et 42 % des filles ont indiqué avoir été dans une voiture conduite par quelqu’un qui consommait de l’alcool. De plus, 28 % des consommateurs occasionnels et une petite proportion d’abstinents ont déclaré « avoir été dans une voiture conduite par une personne qui avait consommé de la marijuana ou d’autres drogues dans les 30 jours précédents. »
Compte tenu de la forte fréquence de conduite à risque, notamment chez les consommateurs fréquents, le projet de légaliser la consommation récréative devrait tenir compte des coûts de mesures d’éducation préventive qui présenteront un portrait précis des risques potentiels liés à la conduite. Les jeunes doivent également comprendre les risques de dépendance. Enfin, il est important de procéder au dépistage et au traitement des troubles liés à la consommation de marijuana.
FREQUENT MARIJUANA USE AND DRIVING RISK BEHAVIOURS IN CANADIAN YOUTH
Jurisdictions across North America are contemplating the legalization of recreational use of marijuana while mitigating potential harms. Currently, marijuana use peaks between ages 15 and 24 years (1); however, many questions remain about the patterns, risks and consequences of marijuana use for this age group. In this study, we examine the characteristics of and driving risks taken by youth with differing patterns of use (i.e., abstainers, occasional users and frequent users).
Youth experience more vehicular crashes than mature operators (2) and crashes may be exacerbated in young drivers if their use of marijuana and driving, with or without alcohol, is prevalent (3). Today’s young drivers have witnessed legalization of medical marijuana, observed the proliferation of dispensaries or retail stores of marijuana products in some cities and experienced the movement toward decriminalization. All of these social changes contribute to a view that marijuana use has few risks (4). Empirically informed educational approaches that provide accurate information to increase awareness and avoidance of risks have shown some success in reducing smoking and alcohol use in young adults (5) and these may also be effective in preventing marijuana-related harms. However, accurate information about harms related to differing patterns of marijuana use in Canadian youth is not available.
In driving simulation studies, marijuana use can increase reaction time, impair road tracking ability and increase difficulty in maintaining constant speed or headway (6). Epidemiological studies suggest that acute marijuana use approximately doubles the risk of crashing (7–9), although this has not been found in all studies (10). Conclusions about the specific effects of marijuana are complicated by the fact that many drivers use marijuana in combination with alcohol (3,11,12). However, young drivers are at higher risk of crashing when sober and their crash risk increases more steeply with any alcohol consumption (13). It is possible that there is a similar relation between crash risk and marijuana use in younger drivers; however, the frequency of driving risk behaviours for youth with different patterns of marijuana use is not known.
Deaths in vehicle crashes are highest from ages 15 to 24. Youth in this age group are also more likely to be involved in fatal crashes as passengers than as drivers (2). In 2012, past year marijuana use was substantially higher for Canadian youth ages 15 to 24 years (20.3%) than for adults older than 25 years (8.4%) and for males (13.7%) than females (7%) (1). Youth ages 15 to 24 were four times more likely to experience harms (i.e., to physical health, relationships, employment, education) from past year marijuana use (5.5%) than adults older than 25 years (1.4%) (1).
On average, marijuana use increases in adolescence and decreases in young adulthood (14–16). However, chronic, increasing and declining patterns of use have been identified (14,15,17,18). There is also growing evidence that a minority of youth experience marijuana use disorders, characterized by tolerance and/or withdrawal symptoms in addition to clinically significant impairments in social relationships and failure to fulfil occupational, academic or home obligations (19). However, differences in the consequences of these patterns of use for driving risks at periods of peak use are not known.
With a large community sample of young adults (ages 22 to 29), we examined their patterns of marijuana use and compared characteristics of use in abstainers, occasional users and frequent users and differences in the frequencies of risks that each group takes as drivers or passengers in motor vehicles.
METHODS
Participants
Data are from the Victoria Healthy Youth Survey (V-HYS). Biannually, from 2003 to 2013, we individually interviewed youth who were randomly recruited from the Greater Victoria Area, British Columbia using random digit dialling to identify families with youth ages 12 to 18 (Mage=15.5, SD=1.9). See Leadbeater et al. (20) for details. At T1 (2003), participants (N=662; 52% females) represented the diverse social economic groups in the population sampled. Most were Caucasian (85%). Response rates were high at each of six interviews (69% to 87%). At the final assessment (T6, 2013), 72% were interviewed (N=478; 55% females; ages 22 to 29 years, Mage=26.8, SD=2.0). Youth lost to follow-up were more likely to be male [T1: 48% versus T6: 45%; χ2(1, 662)=8.77, P=0.003] and to be from lower socioeconomic status (SES) families (T1 SES: M=6.05, SD=1.94) than youth who were retained [T1 SES: M=6.79, SD=1.66; F(1, 636)=19.39, P<0.001].
Measures
Marijuana use
Age at first use
Youth reported the age in years.
Frequency of use in last year
Participants were asked: ‘How often did you use marijuana in the past 12 months?’ on a five-point scale: 0 = never, 1 = a few times a year, 2 = a few times a month, 3 = once a week, and 4 = more than once a week. Using categories established by longitudinal latent class analyses in previous research with this sample (14), we classified youth at each wave as: (1) abstainers (never used marijuana or no use in past 12 months), (2) occasional users (used at most once a week) and (3) frequent users (used more than once a week).
Quantity
Participants were asked: ‘During the last 3 months, on a day when you used marijuana, cannabis or hashish, roughly how many joints did you usually have in that day?’ Youth were also instructed to ‘Count 10 puffs, 5 bong or pipe hits, or ½ gram as equivalent to one joint’ (21).
Heavy episodic drinking
Participants responded to the question: ‘How often in the past 12 months have you had five or more drinks on one occasion?’ (22) as 0 = never, 1 = a few times a year, 2 = a few times a month, 3 = once a week and 4 = more than once a week. The definition of a standard drink was provided.
Marijuana and alcohol use symptoms and disorders
Using the Mini-International Neuropsychiatric Interview (23), responses to 10 items tapping DSM-5 (19) symptoms (both dependency symptoms and abuse-related problems) were coded as YES or NO and summed for marijuana and alcohol use separately. DSM-5 criteria for a substance use disorder, responding YES to two or more items, were used to indicate youth having a substance use disorder.
Polysubstance use
Participants indicated the frequency that they used combinations of marijuana (or hashish) with alcohol and any of the illicit drugs (i.e., cocaine, hallucinogens, amphetamines and club drugs). Responses were re-coded as 0 = never and 1 = ever in the past 6 months.
Marijuana and driving risk behaviours
Participants responded to the following: (1) ‘In the past 12 months, have you been high or intoxicated from marijuana more than once in any situation where you were physically at risk (for example, driving a car, riding a motorbike, using machinery, boating, and so on)?’ and (2) ‘In the past 30 days, how many times were you in a car or other vehicle when the driver (including yourself) had been using marijuana or other drugs?’ For each question, responses coded as 0 = no/never or 1 = yes/ever. Question 1 was asked only at assessments 4 to 6.
Alcohol and driving risk behaviours
Participants responded to the following (24): (1) ‘During the past 30 days, how many times did you drive a car or other vehicle when you had been drinking alcohol?’ and (2) ‘During the past 30 days, how many times did you ride in a car or other vehicle driven by someone, including your parents, who had been drinking alcohol?’ Responses were combined to indicate how many times the youth had been in a car or other vehicle when the driver (including themselves) had been drinking alcohol and coded as 0 = never or 1 = ever.
RESULTS
Peak ages of any past year marijuana use were 18 to 21 for males and females (Figure 1). Marijuana use before age 14 (n=9) was negligible and is not displayed. Sex differences in the marijuana use groups were significant between ages 18 and 27. Proportionately more females than males were abstainers and fewer were frequent users (Figure 1). Based on ‘past year marijuana use’ reported at T6, 37% of males and 52% of females were abstainers, 42% of males and 36% of females were occasional users and 21% of males and 12% of females were frequent users.
As shown in Table 1, male (but not female) frequent users were younger at first use compared with occasional users (but not abstainers). Frequent users consumed more joints at a single occasion, reported more symptoms of a marijuana use disorder and were more likely to meet criteria for a marijuana use disorder. Occasional and frequent users reported similar levels of heavy episodic drinking as well as symptoms and incidence of alcohol use disorders. Most occasional (73% of males and 57% of females) and frequent (81% of males and 82% of females) users reported co-use of marijuana and alcohol within the past 6 months. Frequent users were three times more likely than occasional users to report co-using marijuana and other drugs.
. | Males (n=209) . | Females (n=263) . | ||||
---|---|---|---|---|---|---|
Abstainers (n=78; 37%) . | Occasional users (n=87; 42%) . | Frequent users (n=44; 21%) . | Abstainers (n=136; 52%) . | Occasional users (n=94; 36%) . | Frequent users (n=33; 12%) . | |
Parent SES | 6.96 (1.67) | 7.13 (1.53)b | 6.25 (1.67)c | 6.70 (1.62) | 6.43 (1.86) | 6.47 (1.30) |
Youth SES | 5.18 (2.05)a | 4.98 (1.90)a,b | 4.09 (1.31)c | 5.18 (1.69)a | 4.96 (2.12)a,b | 3.87 (1.82)c |
Age at first use, M (SD) | 15.50† (2.00) | 16.52 (2.88)b | 14.86 (2.61)c | 16.07 (2.71) | 15.96 (2.43) | 15.25 (2.90) |
Quantity (# joints), M (SD) | N/A | 0.92 (1.04)b | 2.42 (2.36)c | N/A | 0.68 (0.68)b | 2.01 (1.19)c |
Marijuana use disorder total symptoms, M (SD) | N/A | 0.98 (1.57)b | 2.64 (1.89)c | N/A | 0.51 (1.21)b | 2.30 (2.47)c |
Marijuana use disorder, % | N/A | 20%b | 68%c | N/A | 11%b | 49%c |
Alcohol use | ||||||
Frequency of HED, M (SD) | 1.22 (1.05)a | 2.08 (1.13)b | 2.00 (1.35)a,b | 0.81 (1.08)a | 1.61 (1.06)b | 1.52 (1.23)a,b |
Alcohol use disorder total symptoms, M (SD) | 1.47 (2.00)a | 2.20 (2.06)a,b | 2.48 (2.44)b | 0.77 (1.41)a | 1.90 (1.79)b | 1.91 (2.36)b |
Alcohol use disorder, % | 36%a | 56%b | 52%a,b | 20%a | 50%b | 42%b |
Polysubstance use, % | ||||||
Marijuana only | N/A | 28% | 16% | N/A | 39%b | 18%c |
Co-use with alcohol | N/A | 73% | 81% | N/A | 57%b | 82%c |
Co-use with other drugs | N/A | 16%b | 42%c | N/A | 13%b | 39%c |
. | Males (n=209) . | Females (n=263) . | ||||
---|---|---|---|---|---|---|
Abstainers (n=78; 37%) . | Occasional users (n=87; 42%) . | Frequent users (n=44; 21%) . | Abstainers (n=136; 52%) . | Occasional users (n=94; 36%) . | Frequent users (n=33; 12%) . | |
Parent SES | 6.96 (1.67) | 7.13 (1.53)b | 6.25 (1.67)c | 6.70 (1.62) | 6.43 (1.86) | 6.47 (1.30) |
Youth SES | 5.18 (2.05)a | 4.98 (1.90)a,b | 4.09 (1.31)c | 5.18 (1.69)a | 4.96 (2.12)a,b | 3.87 (1.82)c |
Age at first use, M (SD) | 15.50† (2.00) | 16.52 (2.88)b | 14.86 (2.61)c | 16.07 (2.71) | 15.96 (2.43) | 15.25 (2.90) |
Quantity (# joints), M (SD) | N/A | 0.92 (1.04)b | 2.42 (2.36)c | N/A | 0.68 (0.68)b | 2.01 (1.19)c |
Marijuana use disorder total symptoms, M (SD) | N/A | 0.98 (1.57)b | 2.64 (1.89)c | N/A | 0.51 (1.21)b | 2.30 (2.47)c |
Marijuana use disorder, % | N/A | 20%b | 68%c | N/A | 11%b | 49%c |
Alcohol use | ||||||
Frequency of HED, M (SD) | 1.22 (1.05)a | 2.08 (1.13)b | 2.00 (1.35)a,b | 0.81 (1.08)a | 1.61 (1.06)b | 1.52 (1.23)a,b |
Alcohol use disorder total symptoms, M (SD) | 1.47 (2.00)a | 2.20 (2.06)a,b | 2.48 (2.44)b | 0.77 (1.41)a | 1.90 (1.79)b | 1.91 (2.36)b |
Alcohol use disorder, % | 36%a | 56%b | 52%a,b | 20%a | 50%b | 42%b |
Polysubstance use, % | ||||||
Marijuana only | N/A | 28% | 16% | N/A | 39%b | 18%c |
Co-use with alcohol | N/A | 73% | 81% | N/A | 57%b | 82%c |
Co-use with other drugs | N/A | 16%b | 42%c | N/A | 13%b | 39%c |
Entries with different lettered superscripts are significantly different from each other (P<0.05). Percentages may not equal 100% due to rounding. HED Heavy episodic drinking; N/A Not applicable; SES Socioeconomic status, as defined by occupational prestige (Hollingshead category)
†Age includes abstainers (n=55 and n=81 for males and females) who indicated that they had used marijuana prior to the last 12 months
. | Males (n=209) . | Females (n=263) . | ||||
---|---|---|---|---|---|---|
Abstainers (n=78; 37%) . | Occasional users (n=87; 42%) . | Frequent users (n=44; 21%) . | Abstainers (n=136; 52%) . | Occasional users (n=94; 36%) . | Frequent users (n=33; 12%) . | |
Parent SES | 6.96 (1.67) | 7.13 (1.53)b | 6.25 (1.67)c | 6.70 (1.62) | 6.43 (1.86) | 6.47 (1.30) |
Youth SES | 5.18 (2.05)a | 4.98 (1.90)a,b | 4.09 (1.31)c | 5.18 (1.69)a | 4.96 (2.12)a,b | 3.87 (1.82)c |
Age at first use, M (SD) | 15.50† (2.00) | 16.52 (2.88)b | 14.86 (2.61)c | 16.07 (2.71) | 15.96 (2.43) | 15.25 (2.90) |
Quantity (# joints), M (SD) | N/A | 0.92 (1.04)b | 2.42 (2.36)c | N/A | 0.68 (0.68)b | 2.01 (1.19)c |
Marijuana use disorder total symptoms, M (SD) | N/A | 0.98 (1.57)b | 2.64 (1.89)c | N/A | 0.51 (1.21)b | 2.30 (2.47)c |
Marijuana use disorder, % | N/A | 20%b | 68%c | N/A | 11%b | 49%c |
Alcohol use | ||||||
Frequency of HED, M (SD) | 1.22 (1.05)a | 2.08 (1.13)b | 2.00 (1.35)a,b | 0.81 (1.08)a | 1.61 (1.06)b | 1.52 (1.23)a,b |
Alcohol use disorder total symptoms, M (SD) | 1.47 (2.00)a | 2.20 (2.06)a,b | 2.48 (2.44)b | 0.77 (1.41)a | 1.90 (1.79)b | 1.91 (2.36)b |
Alcohol use disorder, % | 36%a | 56%b | 52%a,b | 20%a | 50%b | 42%b |
Polysubstance use, % | ||||||
Marijuana only | N/A | 28% | 16% | N/A | 39%b | 18%c |
Co-use with alcohol | N/A | 73% | 81% | N/A | 57%b | 82%c |
Co-use with other drugs | N/A | 16%b | 42%c | N/A | 13%b | 39%c |
. | Males (n=209) . | Females (n=263) . | ||||
---|---|---|---|---|---|---|
Abstainers (n=78; 37%) . | Occasional users (n=87; 42%) . | Frequent users (n=44; 21%) . | Abstainers (n=136; 52%) . | Occasional users (n=94; 36%) . | Frequent users (n=33; 12%) . | |
Parent SES | 6.96 (1.67) | 7.13 (1.53)b | 6.25 (1.67)c | 6.70 (1.62) | 6.43 (1.86) | 6.47 (1.30) |
Youth SES | 5.18 (2.05)a | 4.98 (1.90)a,b | 4.09 (1.31)c | 5.18 (1.69)a | 4.96 (2.12)a,b | 3.87 (1.82)c |
Age at first use, M (SD) | 15.50† (2.00) | 16.52 (2.88)b | 14.86 (2.61)c | 16.07 (2.71) | 15.96 (2.43) | 15.25 (2.90) |
Quantity (# joints), M (SD) | N/A | 0.92 (1.04)b | 2.42 (2.36)c | N/A | 0.68 (0.68)b | 2.01 (1.19)c |
Marijuana use disorder total symptoms, M (SD) | N/A | 0.98 (1.57)b | 2.64 (1.89)c | N/A | 0.51 (1.21)b | 2.30 (2.47)c |
Marijuana use disorder, % | N/A | 20%b | 68%c | N/A | 11%b | 49%c |
Alcohol use | ||||||
Frequency of HED, M (SD) | 1.22 (1.05)a | 2.08 (1.13)b | 2.00 (1.35)a,b | 0.81 (1.08)a | 1.61 (1.06)b | 1.52 (1.23)a,b |
Alcohol use disorder total symptoms, M (SD) | 1.47 (2.00)a | 2.20 (2.06)a,b | 2.48 (2.44)b | 0.77 (1.41)a | 1.90 (1.79)b | 1.91 (2.36)b |
Alcohol use disorder, % | 36%a | 56%b | 52%a,b | 20%a | 50%b | 42%b |
Polysubstance use, % | ||||||
Marijuana only | N/A | 28% | 16% | N/A | 39%b | 18%c |
Co-use with alcohol | N/A | 73% | 81% | N/A | 57%b | 82%c |
Co-use with other drugs | N/A | 16%b | 42%c | N/A | 13%b | 39%c |
Entries with different lettered superscripts are significantly different from each other (P<0.05). Percentages may not equal 100% due to rounding. HED Heavy episodic drinking; N/A Not applicable; SES Socioeconomic status, as defined by occupational prestige (Hollingshead category)
†Age includes abstainers (n=55 and n=81 for males and females) who indicated that they had used marijuana prior to the last 12 months
Substance use and driving risk behaviours
Frequent users reported very high frequencies of driving risk behaviours as drivers or passengers (see Table 2): 80% of males and 75% of females report ‘being in a car driven by driver (including themselves) using marijuana or other drugs in the last 30 days’. Moreover, 64% of males and 33% of females reported that they were ‘intoxicated’ while operating a vehicle. In addition, 50% of the male and 42% of female frequent users reported being in a car driven by a driver using alcohol. In addition, 28% of occasional users and also a small proportion of abstainers reported ‘being in a car driven by a driver using marijuana or other drugs in the last 30 days’. These patterns of relations between marijuana use groups and driving risk behaviours were also stable across age groups (see Figure 2).
. | Males (n=209) . | Females (n=263) . | ||||
---|---|---|---|---|---|---|
Abstainers (n=78; 37%) . | Occasional users (n=87; 42%) . | Frequent users (n=44; 21%) . | Abstainers (n=136; 52%) . | Occasional users (n=94; 36%) . | Frequent users (n=33; 12%) . | |
Have you been high or intoxicated from marijuana more than once in any situation where you were physically at risk (e.g. driving a car, riding a motorbike, using machinery, boating, and so on)? | N/A | 20%b | 64%c | N/A | 10%b | 33%c |
In the past 30 days, have you been in a car or other vehicle when the driver (including yourself) had been using marijuana or other drugs? | 13%a | 28%b | 80%c | 3%a | 28%b | 75%c |
In the past 30 days, have you been in a car or other vehicle when the driver (including yourself) had been drinking alcohol? | 22%a | 37%b | 50%b | 18%a | 31%b | 42%b |
. | Males (n=209) . | Females (n=263) . | ||||
---|---|---|---|---|---|---|
Abstainers (n=78; 37%) . | Occasional users (n=87; 42%) . | Frequent users (n=44; 21%) . | Abstainers (n=136; 52%) . | Occasional users (n=94; 36%) . | Frequent users (n=33; 12%) . | |
Have you been high or intoxicated from marijuana more than once in any situation where you were physically at risk (e.g. driving a car, riding a motorbike, using machinery, boating, and so on)? | N/A | 20%b | 64%c | N/A | 10%b | 33%c |
In the past 30 days, have you been in a car or other vehicle when the driver (including yourself) had been using marijuana or other drugs? | 13%a | 28%b | 80%c | 3%a | 28%b | 75%c |
In the past 30 days, have you been in a car or other vehicle when the driver (including yourself) had been drinking alcohol? | 22%a | 37%b | 50%b | 18%a | 31%b | 42%b |
Entries with different lettered superscripts are significantly different from each other (P<0.05). Percentages may not equal 100% due to rounding. N/A Not applicable
. | Males (n=209) . | Females (n=263) . | ||||
---|---|---|---|---|---|---|
Abstainers (n=78; 37%) . | Occasional users (n=87; 42%) . | Frequent users (n=44; 21%) . | Abstainers (n=136; 52%) . | Occasional users (n=94; 36%) . | Frequent users (n=33; 12%) . | |
Have you been high or intoxicated from marijuana more than once in any situation where you were physically at risk (e.g. driving a car, riding a motorbike, using machinery, boating, and so on)? | N/A | 20%b | 64%c | N/A | 10%b | 33%c |
In the past 30 days, have you been in a car or other vehicle when the driver (including yourself) had been using marijuana or other drugs? | 13%a | 28%b | 80%c | 3%a | 28%b | 75%c |
In the past 30 days, have you been in a car or other vehicle when the driver (including yourself) had been drinking alcohol? | 22%a | 37%b | 50%b | 18%a | 31%b | 42%b |
. | Males (n=209) . | Females (n=263) . | ||||
---|---|---|---|---|---|---|
Abstainers (n=78; 37%) . | Occasional users (n=87; 42%) . | Frequent users (n=44; 21%) . | Abstainers (n=136; 52%) . | Occasional users (n=94; 36%) . | Frequent users (n=33; 12%) . | |
Have you been high or intoxicated from marijuana more than once in any situation where you were physically at risk (e.g. driving a car, riding a motorbike, using machinery, boating, and so on)? | N/A | 20%b | 64%c | N/A | 10%b | 33%c |
In the past 30 days, have you been in a car or other vehicle when the driver (including yourself) had been using marijuana or other drugs? | 13%a | 28%b | 80%c | 3%a | 28%b | 75%c |
In the past 30 days, have you been in a car or other vehicle when the driver (including yourself) had been drinking alcohol? | 22%a | 37%b | 50%b | 18%a | 31%b | 42%b |
Entries with different lettered superscripts are significantly different from each other (P<0.05). Percentages may not equal 100% due to rounding. N/A Not applicable
DISCUSSION
Canadian evidence shows increases in crash risk related to marijuana use (3,8,9). Acceptance of marijuana use is also increasing (4,25). Widespread medical use of marijuana for pain relief, single dose packaging and legalization of recreational use may also contribute to young adults’ beliefs that marijuana is safe and nonaddicting (4).
We investigated marijuana use and driving risk behaviours taken by abstainers, occasional users and frequent users at ages 22 to 29. Two-thirds of the males (63%) and half the females (48%) reported marijuana use in the past 12 months. Youth in the frequent users group (21% of males and 12% of females) used marijuana more than once per week, averaged two joints of marijuana on each occasion, reported more marijuana use disorder symptoms and were more likely to meet criteria for marijuana use disorder, than abstainers and occasional users. Frequent users also co-used marijuana with alcohol and other drugs more than occasional users; 52% of male and 42% of female frequent users as well as 56% of male and 50% of female occasional users also met criteria for alcohol use disorders suggesting co-use is high.
The negative effects of marijuana use on driving risk behaviours have been shown in simulated and real-life conditions (3,6,7,10–13) and the compounding risks for driving associated with combining marijuana with alcohol or other drugs are clear (26). In a driving simulation study with Canadian youth ages 18 to 25, frequency of marijuana use while driving was related to higher speeds reached and more reckless driving (27). The high numbers of youth in the current study who report being in a car driven by a marijuana- or alcohol-using driver in the last 30 days is of concern given motor vehicle crashes are among the most frequent killers of youth and both marijuana and alcohol substantially increase crash risk (2,3). Driving risks in youth may be compounded by fatigue, stress, divided attention and driving inexperience.
It is possible that a portion of youth using marijuana and driving will be detected through greater enforcement of alcohol and driving legislation. However, the capacity of police to detect and sanction marijuana use and driving through breathalyzers or biological tests linking consumption to impairment is limited (28). Educational approaches to harm reduction have shown some success in relation to reducing cigarette smoking and alcohol-related harms (5) and may be useful for addressing marijuana-related harms. Accurate information may be useful in raising young peoples’ awareness of and strategies for reducing harms (29,30). Initiatives targeting youth may also need to address heightened risks related to the widespread co-use of alcohol. Increasing awareness of risks of marijuana use for both drivers and passengers may be important in adolescence and young adulthood. Educational approaches could include adding labels warning against operating a vehicle or machinery while using marijuana to dose packaging and advocating for guidelines established in research on the effects of medical marijuana. The latter propose avoiding driving or operating machinery while experiencing subjective highs and for the following 8 hours (28). Some research suggests that individuals who experience subjective highs enact compensatory behaviours that can reduce risks (e.g., slowing down or increasing following distances). However, as dosages increase, lane weaving, reaction times and difficulties managing cognitive complexity also increase (6). Extending existing graduate license regulations to prohibit driving after any marijuana use for new drivers may enhance awareness of risks. However, graduated licenses regulations for new drivers are unlikely to impact youth older than 18, when marijuana use peaks. Greater funding for education and designated driver campaigns for marijuana users could also reduce impaired driving. Engaging youth in creating and disseminating harm reduction strategies may also improve their impact (29,30).
Youth who develop high levels of marijuana dependency may not be easily influenced by prevention efforts or widespread media campaigns. In the current study, the vast majority of frequent users report being a driver or passenger when the driver (including themselves) used marijuana and 68% of male and 49% of female frequent users met criteria for a marijuana use disorder. Funding for active screening and expanded access to treatment for substance use disorders may be needed to motivate reductions in both use and risky driving behaviours among frequent users who may have both high tolerance and symptoms of dependency.
Limitations
Generalizability is limited to British Columbia, Canada where marijuana use is slightly higher (13.8%) than in other provinces (range = 8.5% to 13.2%) (1). The use of secondary data limits the specificity of questions asked so that risks incurred as passengers or drivers could not be separated. However, there was considerable consistency in patterns of behaviours reported across questions and substances (marijuana and alcohol). Also, questions asked were not specific to motor vehicles. Youth are frequent users of other types of transportation (e.g., bicycles, motorcycles and skate boards). Additional research on the effects of marijuana on crashes specific to these modes of transportation is needed. Finally, vehicle crash frequencies were not available in the data set and the small sample size makes it impossible to control for the many other factors known to increase crash rates in new drivers.
CONCLUSIONS
Our findings of high rates of exposure to driving risks related to marijuana use for British Columbia youth indicate a failure of current programs and speak to an urgent need for better prevention and intervention strategies to reduce impaired driving or riding with an impaired driver. If legalization of recreational use occurs, expenditures should be directed at evidence-informed education that presents an accurate picture of potential harms. Our research suggests that youth need more knowledge of risks for marijuana dependency and risk of using marijuana in combination with alcohol or other drugs. Professional bodies like the Canadian Medical Association and Canadian Paediatric Society could assist in the development and dissemination of these materials.
Acknowledgements
This project was approved by the University of Victoria Human Research Ethics Board (protocol #09-292). The Victoria Healthy Youth Survey study and this research were supported by grants from the Canadian Institutes of Health Research (#43275, #79917, #93533, #130500), a Vancouver Island Health Collaborative research grant and the Victoria CRD Traffic Safety Commission. The authors have no conflict of interest(s) to declare.
References
Author notes
Correspondence: Megan E. Ames, University of Victoria, Cornett Building B332, 3800 Finnerty Road, Victoria, British Columbia V8P 5C2. E-mail: mames@uvic.ca